This present disclosure relates to slide-out rooms, particularly the trim flange that goes around the outside wall of the slide-out. Slide-out rooms reside in an opening in the side wall of an RV, trailer, or other mobile living quarters. The slide-out room provides additional living or storage space when the RV is parked without increasing the overall footprint of the vehicle. The slide-out room must be properly sealed from the outside elements, whether it is in the extended position or the retracted position. Typically, the room is sealed with a face seal that goes around the perimeter of the opening in the sidewall, along with wiper seals that slide on the sidewalls of the room as the room moves in or out. In order to have a mating surface for the face seal, a flange is attached to the perimeter of the outside wall of the slide-out room. Currently this is accomplished through a long extrusion with mitered corners that is attached to the slide-out room. The corners are subsequently covered up and protected with decorative trim pieces. Mitering corners on a room that can be quite large requires precision measurement and attachment to the room. A high level of skill is required. Cutting the extrusion too short or too long results in poor fitment, leaks, and bad aesthetics. Further, the trim pieces are held in with screws that require drilling and tapping to be properly attached to the extrusion. The screws must be no longer than the thickness of the extrusion and trim piece, as any part that extends too far could damage the seal, side wall, or prevent proper closure of the slide-out room. Due to the extreme time pressure when manufacturing an RV, an improved flange system is needed.